Metal gate stack having TaAlCN layer

ABSTRACT

Gate stacks for improving integrated circuit device performance and methods for fabricating such gate stacks are disclosed herein. An exemplary method includes forming a gate stack over a substrate and at least partially removing the gate stack, thereby forming an opening. A multi-function layer is deposited in the opening and a work function layer is deposited over the multi-function layer. The multi-function layer includes nitrogen and one of titanium or tantalum. The work function layer includes nitrogen and one of titanium or tantalum. A concentration of the nitrogen of the work function layer is different than a concentration of the nitrogen of the multi-function layer. In some implementations, the concentration of the nitrogen of the work function layer from about 2% to about 5% and the concentration of the nitrogen of the multi-function layer from about 5% to about 15%.

This application is a continuation of U.S. patent application Ser. No.15/149,978, filed May 9, 2016, now U.S. Pat. No. 10,032,634, which is adivisional of U.S. patent application Ser. No. 14/532,228 filed Nov. 4,2014, now U.S. Pat. No. 9,337,192, which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/056,278, filed Sep. 26, 2014,and is a continuation-in-part of U.S. patent application Ser. No.14/328,299, filed Jul. 10, 2014, now U.S. Pat. No. 9,337,303, which is acontinuation-in-part of U.S. patent application Ser. No. 13/244,355,filed Sep. 24, 2011. The entire disclosures of each of the above listedapplications are hereby incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. These advances have increased thecomplexity of processing and manufacturing ICs and, for these advancesto be realized, similar developments in IC processing and manufacturingare needed. In the course of IC evolution, functional density (i.e., thenumber of interconnected devices per chip area) has generally increasedwhile geometry size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling downprocess generally provides benefits by increasing production efficiencyand lowering associated costs. Such scaling down has also increased thecomplexity of processing and manufacturing ICs and, for these advancesto be realized, similar developments in IC processing and manufacturingare needed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for only illustrationpurposes. In fact, the dimensions of the various features may bearbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flow chart of a method for fabricating an integrated circuitdevice according to various aspects of the present disclosure.

FIGS. 2, 3, 4, 5, 6, and 7 are diagrammatic cross-sectional views of anintegrated circuit device during various stages of the method of FIG. 1according to various aspects of the present disclosure.

FIGS. 8, 9, 10, and 11 are diagrammatic cross-sectional views of anintegrated circuit device constructed according to various embodiments.

FIG. 12 is diagrammatic top view of an integrated circuit device inaccordance with some embodiments.

FIGS. 13 and 14 are diagrammatic cross-sectional views of the integratedcircuit device of FIG. 12 in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

FIG. 1 is a flow chart of a method 100 for fabricating an integratedcircuit device, in portion or entirety, according to various aspects ofthe present disclosure. The method 100 begins at block 110 where a gatestructure is formed over a substrate. The gate structure has a gatestack that includes a high-k dielectric layer disposed over thesubstrate and a dummy gate disposed over the high-k dielectric layer. Atblock 120, the dummy gate is removed from the gate structure to form anopening therein. At block 130, a multi-function blocking/wetting layer,a work function layer, and a conductive layer are formed to fill theopening. The multi-function blocking/wetting layer is formed over thehigh-k dielectric layer, the work function layer is formed over themulti-function blocking/wetting layer, and the conductive layer isformed over the work function layer. The multi-function blocking/wettinglayer includes a material that sufficiently prevents (or reduces) metalimpurities from penetrating the high-k dielectric layer (for example,from the conductive layer) during processing, while providing sufficientwettability (in other words, desired interface quality) with the workfunction layer. The method 100 may continue at block 140 to completefabrication of the integrated circuit device. Additional steps can beprovided before, during, and after the method 100, and some of the stepsdescribed can be replaced or eliminated for additional embodiments ofthe method 100.

In some embodiments, between the operation 110 and the operation 120,the source and drain features may be formed in the active regions onboth sides of the dummy gate. In one example, an ion implantationprocess is performed to introduce dopant (such as phosphorous) to formthe source and drain features and an annealing process may be followedto activate the dopant. In another example, a procedure is implementedto form source and drains. The procedure may include performing a firstion implantation process to form lightly doped drain (LDD) features;forming gate spacers by deposition and anisotropic etching; performing asecond ion implantation process to form heavily doped source and drainsaligned with the gate spacers; and an annealing process is followed toactivate the dopant. In another example, source and drain are formedwith strain effect by a proper procedure. The procedure may include: thesubstrate in the source and drain regions is etched to be recessed; anda semiconductor material different from that of the substrate isepitaxially grown in the recesses by selective epitaxy growth within-situ doping. The semiconductor material is chosen to provide properstrain to the channel to enhance mobility, such as tensile strain ton-channel field effect transistor by using silicon carbide andcompressive strain to p-channel field effect transistor by using silicongermanium.

The method 100 may have various embodiments. In some embodiments, themethod 100 may alternatively implement a high-k last process, in whichthe high-k dielectric layer is formed after the removal of the dummygate. In furtherance of the embodiments, at block 110, a gate stackincluding gate dielectric (such as silicon oxide) and gate electrode(such as polysilicon) are deposited and patterned. At block 120, boththe gate dielectric and gate electrode are removed, resulting in a gatetrench. At block 130, a high-k dielectric layer and gate electrode areformed in the gate trench by deposition and polishing such as chemicalmechanical polishing (CMP). The gate electrode includes a multi-functionblocking/wetting layer, a work function layer, and a conductive layer.

FIGS. 2-7 are diagrammatic cross-sectional views of an integratedcircuit device 200, in portion or entirety, at various stages offabrication according to the method 100 of FIG. 1. FIGS. 2-7 have beensimplified for the sake of clarity to better understand the inventiveconcepts of the present disclosure. The integrated circuit device 200 isdescribed with reference to FIGS. 2-7 and method 100 is furtherdescribed in details as well in accordance with some embodiments.

In the depicted embodiment, the integrated circuit device 200 includes afield-effect transistor device, such as an n-channel field effecttransistor (NFET) or a p-channel field effect transistor (PFET). Theintegrated circuit device 200 may be included in memory cells and/orlogic circuits that include passive components such as resistors,capacitors, inductors, and/or fuses; active components, such asmetal-oxide-semiconductor field effect transistors (MOSFETs),complementary metal-oxide-semiconductor transistors (CMOSs), highvoltage transistors, and/or high frequency transistors; other suitablecomponents; or combinations thereof. Additional features can be added inthe integrated circuit device 200, and some of the features describedbelow can be replaced or eliminated in other embodiments of theintegrated circuit device 200.

In FIG. 2, the integrated circuit device 200 includes a substrate 210.In the depicted embodiment, the substrate 210 is a semiconductorsubstrate including silicon. Alternatively or additionally, thesubstrate 210 includes another elementary semiconductor, such asgermanium; a compound semiconductor including silicon carbide, galliumarsenic, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs,AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. In yetanother alternative, the substrate 210 is a semiconductor on insulator(SOI). In other alternatives, semiconductor substrate 210 may include adoped epi layer, a gradient semiconductor layer, and/or a semiconductorlayer overlying another semiconductor layer of a different type, such asa silicon layer on a silicon germanium layer. The substrate 210 includesvarious doping configurations depending on design requirements of theintegrated circuit device 200. For example, the substrate 210 mayinclude various doped regions doped with p-type dopants, such as boronor BF₂; n-type dopants, such as phosphorus or arsenic; or combinationsthereof. The doped regions may be formed on the semiconductor substrate,in a P-well structure, in a N-well structure, or in a dual-wellstructure.

An isolation feature 212 is disposed in the substrate 210 to isolatevarious regions and/or devices of the substrate 210. The isolationfeature 212 utilizes isolation technology, such as local oxidation ofsilicon (LOCOS) and/or shallow trench isolation (STI), to define andelectrically isolate the various regions. The isolation feature 212includes silicon oxide, silicon nitride, silicon oxynitride, othersuitable dielectric materials, or combinations thereof. The isolationfeature 212 is formed by any suitable process. As one example, formingSTI features includes using a lithography process to expose a portion ofthe substrate, etching a trench in the exposed portion of the substrate(for example, by using a dry etching and/or wet etching), filling thetrench (for example, by using a chemical vapor deposition process) withone or more dielectric materials, and planarizing the substrate andremoving excessive portions of the dielectric material(s) by a polishingprocess, such as CMP. In some examples, the filled trench may have amulti-layer structure, such as a thermal oxide liner layer filled withsilicon nitride or silicon oxide.

In some embodiments, the semiconductor substrate has a non-planar activeregion, such as fin-like active regions (or a fin structure). A fin-likeactive region is a feature of a semiconductor material extruding abovethe planar surface of the semiconductor substrate and provides multiplesurface coupling between a gate and a corresponding channel. Thesemiconductor material of the fin-like active regions may the samesemiconductor material of the semiconductor substrate or alternatively asemiconductor material different from that of the substrate. In someexamples, the fin-like active regions may be formed by etching torecessing the STI features or epitaxially growing a semiconductormaterial on the semiconductor substrate using a proper technique, suchas selective epitaxy growth.

A gate structure 220 is disposed over the substrate 210. In the depictedembodiment, the gate structure 220 includes a gate stack having aninterfacial dielectric layer 222, a high-k dielectric layer 224, and adummy gate layer 226. The interfacial dielectric layer 222 and thehigh-k dielectric layer 224 may collectively be referred to as a gatedielectric layer of the gate structure 220. The gate stack may includeadditional layers, such as a capping layer, a diffusion/barrier layer, adielectric layer, a metal layer, other suitable layers, or combinationsthereof. The gate structure 220 is formed by a process that includesdeposition processes, lithography patterning processes, etchingprocesses, other suitable processes, or combinations thereof. Thedeposition processes include physical vapor deposition (PVD), chemicalvapor deposition (CVD), atomic layer deposition (ALD), plasma enhancedCVD (PECVD), remote plasma CVD (RPCVD), molecular organic CVD (MOCVD),sputtering, plating, other suitable methods, or combinations thereof.The lithography patterning processes include resist coating (forexample, spin-on coating), soft baking, mask aligning, exposure,post-exposure baking, developing the photoresist, rinsing, drying (forexample, hard baking), other suitable processes, or combinationsthereof. The lithography exposure process may be implemented or replacedby other proper methods such as maskless lithography, electron-beamwriting, ion-beam writing, and molecular imprint. The etching processesinclude dry etching, wet etching, or combinations thereof. In someembodiments, the gate structure 220 is formed by a procedure thatincludes depositing various gate material layers; forming a patternedresist layer by lithography patterning process; etching the gatematerial layers to form the gate structure 220 using the patternedresist layer as an etch mask; and removing the patterned resist layer bywet stripping or plasma ashing. In some other embodiments, a hard masklayer, such as silicon nitride, may be used as an etch mask during theetching process to pattern the gate material layers. In this case, theprocedure to form the gate structure 220 includes depositing variousgate material layers; depositing a hard mask layer on the gate materiallayers; forming a patterned resist layer by lithography patterningprocess; etching to pattern the hard mask layer using the patternedresist layer as an etch mask; and etching the gate material layers toform the gate structure 220 using the patterned hard mask layer as anetch mask.

The interfacial dielectric layer 222 is disposed over the substrate 210.In an example, the interfacial dielectric layer 222 has a thickness ofabout 5 Å to about 20 Å. In the depicted embodiment, the interfacialdielectric layer 222 is an oxide-containing layer, such as a siliconoxide (SiO₂) layer or a silicon oxynitride (SiON) layer. The interfaciallayer 222 may include other suitable materials. The interfacialdielectric layer 222 is formed by a chemical oxide technique, thermaloxide technique, atomic layer deposition (ALD), chemical vapordeposition (CVD), or other suitable technique. A cleaning process, suchas an HF-last pre-gate cleaning process (for example, using ahydrofluoric (HF) acid solution), may be performed before theinterfacial dielectric layer 222 is formed over the substrate 210.

The high-k dielectric layer 224 is disposed over the interfacialdielectric layer 222, and the dummy gate layer 226 is disposed over thehigh-k dielectric layer 224. A thickness of the high-k dielectric layer224 and the dummy gate layer 226 depends on design requirements of theintegrated circuit device 200. In an example, the high-k dielectriclayer 224 has a thickness of about 5 Å to about 30 Å, and the dummy gatelayer has a thickness of about 350 Å to about 700 Å. The high-kdielectric layer 224 includes a high-k dielectric material, such asHfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, zirconium oxide, aluminumoxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, other suitable high-kdielectric materials, or combinations thereof. The dummy gate layer 226includes a material suitable for a gate replacement process. Forexample, in the depicted embodiment, the dummy gate layer 226 includepolysilicon.

The gate structure 220 further includes spacers 228 formed by a suitableprocess. For example, a dielectric layer, such as a silicon nitridelayer, is blanket deposited over the integrated circuit device 200; andthen, the silicon nitride layer is anisotropically etched to remove thesilicon nitride layer to form spacers 228 as illustrated in FIG. 2. Thespacers 228 are positioned adjacent sidewalls of the gate stack(interfacial dielectric layer 222, high-k dielectric layer 224, anddummy gate layer 226) of the gate structure 220. Alternatively oradditionally, the spacers 228 include another dielectric material, suchas silicon oxide, silicon carbon nitride, or combinations thereof.

Various source/drain features 230 may be disposed in the substrate 210.The source/drain features 230 are interposed by the gate structure 220.The source/drain features 230 may include lightly doped source and drain(LDD) regions and/or heavily doped source and drain (HDD) regions. TheLDD and/or HDD regions may be formed by ion implantation or diffusion ofn-type dopants, such as phosphorous or arsenic, or p-type dopants, suchas boron or BF₂. An annealing process, such as a rapid thermal annealingand/or a laser thermal annealing, may be performed to activate dopantsof the LDD and/or HDD regions. The LDD and/or HDD regions may be formedat any time in the depicted embodiment. The source/drain features 230may include raised source/drain features, such as epitaxial features(for example, silicon germanium epitaxial features or silicon epitaxialfeatures). Silicide features may be disposed over the source/drainfeatures 230, for example, to reduce contact resistance. The silicidefeatures may be formed over the source and drain features by aself-aligned salicide process, which can include depositing a metallayer, annealing the metal layer such that the metal layer is able toreact with silicon to form silicide, and then removing the non-reactedmetal layer.

A dielectric layer 232 is disposed over the substrate 210, such as aninterlayer (or inter-level) dielectric (ILD) layer. The dielectric layer232 includes a dielectric material, such as silicon oxide, siliconnitride, silicon oxynitride, tetraethylorthosilicate (TEOS) formedoxide, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG),low-k dielectric material, other suitable dielectric material, orcombinations thereof. Exemplary low-k dielectric materials includefluorinated silica glass (FSG), carbon doped silicon oxide, BlackDiamond® (Applied Materials of Santa Clara, Calif.), Xerogel, Aerogel,amorphous fluorinated carbon, Parylene, BCB (bis-benzocyclobutenes),SiLK (Dow Chemical, Midland, Mich.), polyimide, other proper materials,and/or combinations thereof. The dielectric layer 232 may include amultilayer structure including multiple dielectric materials. Thedielectric layer 232 is formed by a suitable process to a suitablethickness, including by CVD, high density plasma CVD, spin-on, and/orother suitable methods. Subsequent to the deposition of the dielectriclayer 232, a chemical mechanical polishing (CMP) process is performeduntil a top portion of the gate structure 220 is reached/exposed.Particularly, a top portion of the gate stack of the gate structure 220(here, the dummy gate layer 226) is exposed as illustrated in FIG. 2.Additional layers may be formed overlying and/or underlying thedielectric layer 232.

In FIGS. 3-7, a gate replacement process is performed, where the dummygate layer 226 is replaced with a metal gate. In FIG. 3, the dummy gatelayer 226 is removed from the gate stack of the gate structure 220,thereby forming an opening (or gate trench) 240. The opening 240 exposesthe high-k gate dielectric layer 224. The dummy gate layer 226 may beremoved by an etching process, other suitable process, or combinationsthereof. In an example, an etching process selectively etches the dummygate layer 226.

In FIG. 4, a multi-function blocking/wetting layer 242 is formed overthe substrate 210, such that the multi-function blocking/wetting layer242 layer partially fills the opening 240. The multi-functionblocking/wetting layer 242 is disposed along sidewalls of the gatestructure 220 that define the opening 240. In the depicted embodiment,the multi-function blocking/wetting layer 242 is disposed over thehigh-k dielectric layer 224. In an example, the multi-functionblocking/wetting layer 242 has a thickness of about 30 Å to about 100 Å.The multi-function blocking/wetting layer 242 functions as both ablocking (or barrier) layer and a wetting layer during processing. Forexample, the multi-function blocking/wetting layer 242 prevents orreduces metal impurities from penetrating any dielectric layers disposedbelow the multi-function blocking/wetting layer 242 (such as the gatedielectric of the gate stack of the gate structure 220) while enhancingadhesion between the layer underneath it and the layer above it. It alsoprovides desirable interface quality between the multi-functionblocking/wetting layer 242 and any material layer formed over themulti-function blocking/wetting layer 242. Accordingly, in the depictedembodiment, the multi-function blocking/wetting layer 242 prevents orreduces metal impurities from penetrating into the high-k dielectriclayer 224 and the interfacial dielectric layer 222, while enhancingadhesion between layers beneath and above it, such as the high-kdielectric layer 224 and a layer of the gate stack of the gate structure220 that is formed over the multi-function blocking/wetting layer 242(such as the work function layer 244). Such functionality is describedin further detail below.

In the depicted embodiment, the multi-function blocking/wetting layer242 includes tantalum aluminum nitride (TaAlN), and in exemplaryembodiments the TaAlN is present as tantalum aluminum carbon nitride(TaAlCN). An atomic concentration of nitrogen and carbon of the TaAlCNlayer is optimized, such that the multi-function blocking/wetting layer242 adequately prevents or reduces metal impurities from penetratingunderlying dielectric layers (for example, high-k dielectric layer 224and interfacial layer 222) while minimally effecting a work function ofthe integrated circuit device 200. Thus, the nitrogen atomicconcentration and carbon atomic concentration are chosen to balance theblocking capability and the desired work function. In the depictedembodiment, the TaAlCN layer includes a nitrogen atomic concentration ofabout 5% to about 15% and a carbon atomic concentration of about 5% toabout 20%. At lower nitrogen and carbon atomic concentrations (forexample, lower than about 5%), the blocking capability can move in anundesired direction, while shifting closer to the desired work function.On the other hand, at higher nitrogen and carbon atomic concentrations(for example, nitrogen atomic concentrations of greater than 15% andcarbon atomic concentrations of greater than 20%), the balance shiftsaway from the desired work function and moves toward the desiredblocking capability. In the depicted embodiment, the TaAlCN ratioincludes a Ta:Al ratio that enhances interface quality (which can bereferred to as wettability) between the multi-function blocking/wettinglayer 242 and an overlying layer that includes aluminum. For example,the TaAlCN layer 242 includes a Ta:Al ratio of about 1:1 to about 1:3.

The process used to form the multi-function blocking/wetting layer 242,here, the TaAlCN layer, is tuned to achieve optimal blocking andwettability functionality of the multi-function blocking/wetting layer242. In the depicted embodiment, a physical vapor deposition (PVD) isused to form the multi-function blocking/wetting layer 242. Variousprocess parameters of the PVD process, such as substrate temperature,gas type, gas flow rate, chamber pressure, DC power, bias power, processtime, other suitable parameters, or combinations thereof, are tuned toachieve the desired blocking and wettability functionality.Alternatively, an atomic layer deposition (ALD) is used to form themulti-function blocking/wetting layer 242. Various process parameters ofthe ALD process, such as substrate temperature, gas type, gas flow rate,chamber pressure, process time, other suitable parameters, orcombinations thereof, are tuned to achieve the desired blocking andwettability functionality. Alternatively, the multi-functionblocking/wetting layer 242 are formed by other processes, such aschemical vapor deposition (CVD), plasma enhanced CVD (PECVD), remoteplasma CVD (RPCVD), molecular organic CVD (MOCVD), PVD, ALD, plating,other suitable method, or combinations thereof. Various processparameters of such alternative processes may be tuned to achieve thedesired blocking and wettability functionality of the multi-functionblocking/wetting layer 242.

In the depicted embodiment, a high pressure PVD process, which maintainsthe chamber pressure of about 0.1 Torr to about 5 Torr, deposits themulti-function blocking/wetting layer 242 at a temperature of about 250°C. to about 450° C. The high pressure PVD process can ensure that themulti-function blocking/wetting layer 242 adequately, partially fillsthe opening 240. The high pressure PVD process provides adequatecoverage, for example, for high aspect ratio openings, such as theopening 240. For example, in the depicted embodiment, high aspect ratioopenings refer to openings having a height to width ratio greater thanor equal to 2.2 (height/width≥2.2). Alternatively, high aspect ratioopenings may be defined by other height to width ratios.

In another embodiment, the multi-function blocking/wetting layer 242includes multiple TaAlCN layers with different N %. For example, abottom TaAlCN layer has a higher N %, such as from about 5% to about15%, and a top TaAlCN layer has a lower N %, such as from about 2% toabout 5%. In this case, the bottom TaAlCN layer serves mainly as ablocking layer while the top TaAlCN layer servers mainly as a workfunction layer. By choosing a proper C % and N %, an optimized blockingcapability is achieved. In an example, C % is in a range from about 5%to about 20%, while the N % is in a range from about 5% to 15%.

In FIG. 5, a work function layer 244 is formed over the substrate 210,such that work function layer 244 partially fills the opening 240. Inthe depicted embodiment, the work function layer 244 is disposed overthe multi-function blocking/wetting layer 242. In an example, the workfunction layer 244 has a thickness of about 30 Å to about 100 Å. Inanother example, the work function layer 244 disposed on themulti-function blocking/wetting layer 242 has a thickness of about 30 Åto about 100 Å, and the work function layer 244 disposed along sidewallsof the opening 240 may have a thickness less than 30 Å, or a thicknessof about 30 Å to about 100 Å. The work function layer 244 includes amaterial that can be tuned to have a proper work function for enhancedperformance of the associated device. For example, if a p-typefield-effect transistor (PFET) device, the work function layer 244includes a p-type work function material that can be configured to havea desired work function value (such as close to 5.2 eV or in a rangefrom 4.7 eV to 5 eV) for the gate electrode of the PFET. On the otherhand, if an n-type field-effect transistor (NFET) device, the workfunction layer 244 includes an n-type work function material (such asTaAlCN) that can be configured to have a desired work function value(such as close to 4.2 eV or in a range from 4.1 eV to 4.5 eV) of thegate electrode of the NFET. The work function layer 244 is formed by aphysical vapor deposition (PVD), chemical vapor deposition (CVD), atomiclayer deposition (ALD), plasma enhanced CVD (PECVD), remote plasma CVD(RPCVD), molecular organic CVD (MOCVD), sputtering, plating, othersuitable method, or combinations thereof.

In some embodiments, the TaAlCN layer is formed using a precursor thatincludes a tantalum-based chemical, an aluminum-based chemical, acarbon-based gas and a nitrogen-based gas. In some examples, thetantalum-based chemical includes pentakis-(dimethylamino) tantalum(PDMAT), triethylaluminum, tantalum chloride (TaC15), other suitableTa-containing chemical or a combination thereof. In some examples, thealuminum-based chemical includes triethylaluminum (TEAl),Trimethylaluminium (TMA), aluminum borohydride trimethylamine (AlBT),other suitable Al-containing chemical or a combination thereof. In someexamples, the nitrogen-based gas includes NH3, N2, other suitableN-containing chemical or a combination thereof. In some examples, thecarbon-based gas includes CHx, such as CH3.

In some embodiments, the work function layer 244 is an n work functionlayer that includes TaAlCN. In the depicted embodiment, the workfunction layer 244 includes TaAlCN that has a different composition thanthe TaAlCN in the multi-function blocking/wetting layer 242. Forexample, the nitrogen atomic concentration in the work function layer244 is lower than the nitrogen atomic concentration in themulti-function blocking/wetting layer 242. The nitrogen atomicconcentration is chosen to balance the blocking capability and thedesired work function. In an embodiment, the nitrogen atomicconcentration in the work function layer 244 is about 2% to about 5%.Aluminum in the work function layer 244 has a high mobility and caneasily penetrate an under layer when the nitrogen atomic concentrationis lower (e.g., less than about 2%). At higher nitrogen atomicconcentrations (e.g., higher than about 2%), the nitrogen in the workfunction layer 244 can bond to the aluminum, form a stable phase, andreduce the penetration of aluminum into an under layer. Even highernitrogen atomic concentrations (e.g., higher than about 5%), however,can cause a shift away from a target or desired work function.

In some embodiments, the work function layer 244 is an n work functionlayer for NFET and having a work function ranging from about 4.1 eV toabout 4.5 eV. In furtherance of the embodiments, the n work functionlayer includes titanium (Ti), aluminum (Al), titanium aluminum (TiAl),tantalum (Ta), or zirconium silicon (ZrSi₂).

In FIG. 6, a conductive layer 246 is formed over the substrate 210, suchthat the conductive layer 246 partially fills the opening 240. Theconductive layer 246 is disposed over the work function layer 244. In anexample, the conductive layer 246 has a thickness of about 300 Å toabout 1,500 Å. In the depicted embodiment, the conductive layer 246includes aluminum. Alternatively or additionally, the conductive layer246 includes copper, tungsten, a metal alloy, a metal silicide, otherconductive material, or combinations thereof. The conductive layer 246is formed by a physical vapor deposition (PVD), chemical vapordeposition (CVD), atomic layer deposition (ALD), plasma enhanced CVD(PECVD), remote plasma CVD (RPCVD), molecular organic CVD (MOCVD),sputtering, plating, other suitable method, or combinations thereof.

In FIG. 7, a chemical mechanical polishing (CMP) process is performeduntil the dielectric layer 232 is reached or exposed. The CMP processthus removes portions of the multi-function blocking/wetting layer 242,work function layer 244, and the conductive layer 246 that are disposedover the dielectric layer 232. The remaining portions of themulti-function blocking/wetting 242, work function layer 244, and theconductive layer 246 combine to fill the opening 240, such that the gatestack of the gate structure 220 includes the interfacial dielectriclayer 222, the high-k dielectric layer 224, the multi-functionblocking/wetting 242, work function layer 244, and the conductive layer246. The multi-function blocking/wetting layer 242, the work functionlayer 244, and the conductive layer 246 may collectively be referred toas a gate electrode of the gate structure 220.

The integrated circuit device 200 may include other features. Forexample, a multilayer interconnection (MLI) including metal layers andinter-metal dielectric (IMD) layers may be formed over the substrate210, such as over the dielectric layer 232, to electrically connectvarious features or structures of the integrated circuit device 200. Themultilayer interconnection includes vertical interconnects, such as viasor contacts, and horizontal interconnects, such as metal lines. In anexample, the MLI includes interconnection features to the source/drainfeatures 230 and/or the gate stack of the gate structure 220. Thevarious interconnection features include various conductive materialsincluding aluminum, copper, titanium, tungsten, alloys thereof, silicidematerials, other suitable materials, or combinations thereof. In anexample, a damascene process or dual damascene process is used to form acopper or aluminum multilayer interconnection structure.

The integrated circuit device 200 exhibits reduced leakage current,leading to improved device performance. Such reduced leakage current andimproved device performance may be achieved by multi-functionblocking/wetting layer 242 in the gate stack of the gate structure 220.The multi-function blocking/wetting layer 242 can sufficiently blockmetal impurities from penetrating underlying dielectric layers, whileproviding sufficient wettability (interface quality) to overlyinglayers.

The integrated circuit device 200 and the method 100 making the same mayhave other embodiments without departure from the scope of the presentdisclosure. A few of embodiments are provided below. The similarfeatures and similar operations are not repeated for simplicity.

FIG. 8 illustrates an integrated circuit device 200 in accordance withsome embodiments. The integrated circuit device 200 further includes acapping layer 250 disposed between the high-k dielectric layer 224 andthe multi-function blocking/wetting layer 242. The capping layer 250further protects the high-k dielectric layer and/or reinforces thefunctions of the multi-function blocking/wetting layer 242. The cappinglayer 250 includes titanium nitride (TiN), tantalum nitride (TaN), or acombination thereof. The capping layer may be formed by a suitabletechnique, such as PVD. The capping layer may be formed at the operation110 or alternatively at the operation 130 of the method 100. In someembodiments when the high-k dielectric layer 224 is formed at theoperation 110, the capping layer 250 may be formed at the operation 110as well, therefore protecting the high-k dielectric layer through thefabrication. In this case, both the high-k dielectric layer 224 and thecapping layer 250 are only formed in the bottom of the opening 240 whilethe multi-function blocking/wetting layer 242 and the work functionlayer 244 are disposed on bottom and sidewalls of the opening 240, orare U-shaped in other words, as illustrated in FIG. 8. When the method100 uses a high-k last process, the high-k dielectric layer is alsoformed at operation 130. In this case, the capping layer 250 is formedat the operation 130 as well. Therefore, both the high-k dielectriclayer 224 and the capping layer 250 are formed on the sidewalls and areU-shaped.

FIG. 9 illustrates an integrated circuit device 200 in accordance withsome embodiments. The method 100 uses a high-k last process, the high-kdielectric layer is formed at operation 130 after the removal dummy gatestack by the operation 120. In this case, the dummy gate formed by theoperation 110 may include a silicon oxide layer and a polysilicon layerover the silicon oxide layer. At the operation 120, the gate stack isremoved by etching. Then the gate dielectric layer is formed in theopening 240 at the operation 130. Other gate material layers (such as242, 246 and 248) are formed in the opening 240 in a similar way, suchas those steps to form the material layer 242, 244 and 248 describedabove. Accordingly, the high-k dielectric layer is U-shaped as well.Again, of the capping layer 250 is present between the high-k dielectriclayer 224 and the multi-function blocking/wetting layer 242, both thehigh-k dielectric layer 224 and the capping layer 250 are formed on thesidewalls and are U-shaped. The interfacial layer 222 may be removed atoperation 120 and re-deposited at operation 130, such as by thermaloxidation (not U-shaped) or ALD (U-shaped).

FIG. 10 illustrates an integrated circuit device 200 in accordance withsome embodiments. The source and drain (S/D) features 230 are formedwith different semiconductor material for strain effect, enhancing thechannel mobility and device performance. At the operation 120, thesource and drain features 230 are formed by a proper procedure. Forexample, the procedure may include: the substrate in the source anddrain regions is etched to be recessed; and a semiconductor materialdifferent from that of the substrate is epitaxially grown in therecesses by selective epitaxy growth with in-situ doping. Thesemiconductor material is chosen to provide proper strain to the channelto enhance mobility, such as tensile strain to n-channel field effecttransistor by using silicon carbide and compressive strain to p-channelfield effect transistor by using silicon germanium. In one example, thedevice 200 is an nFET, the semiconductor material is silicon carbidedoped with phosphorous for S/D features 230 while the substrate 210 is asilicon substrate. In one example, the device 200 is a pFET, thesemiconductor material is silicon germanium doped with boron for S/Dfeatures 230 while the substrate 210 is a silicon substrate. In anotherexample, the integrated circuit device 200 includes an nFET and a pFET,silicon carbide with phosphorous dopant is epitaxially grown to form S/Dfeatures 230 for the nFET, silicon germanium with boron dopant isepitaxially grown to form S/D features 230 for the pFET while thesubstrate 210 is a silicon substrate. The S/D features 230 may beepitaxially grown such that the top surface of the S/D features 230 issubstantially coplanar with the top surface of the semiconductorsubstrate 210. Alternatively, the S/D features 230 may be epitaxiallygrown beyond the top surface of the semiconductor substrate 210, asillustrated in FIG. 10.

FIG. 11 illustrates an integrated circuit device 200 in accordance withsome embodiments. In FIG. 11, the gate stack 220 includes themulti-function blocking/wetting layer 242 on the high-k dielectric layer224 and a conductive layer 246 directly on the multi-functionblocking/wetting layer 242. The conductive layer 246 may be aluminum forexamples. The multi-function blocking/wetting layer 242 includes TaAlCNand is tuned to function as n work function metal layer as well. Anatomic concentration of nitrogen and carbon of the TaAlCN layer isoptimized, such that the multi-function blocking/wetting layer 242adequately prevents or reduces metal impurities from penetratingunderlying dielectric layers (for example, high-k dielectric layer 224and interfacial layer 222) while having a proper work function, such asa work function ranging from about 4.1 eV to about 4.5 eV. In thedepicted embodiment, the TaAlCN layer includes a nitrogen atomicconcentration of about 3% to about 10%. The TaAlCN layer may include acarbon atomic concentration of about 5% to about 20%. The TaAlCN ratiomay include a Ta:Al ratio that enhances interface quality (which can bereferred to as wettability) between the multi-function blocking/wettinglayer 242 and an overlying layer that includes aluminum. For example,the TaAlCN layer 242 includes a Ta:Al ratio of about 1:1 to about 1:3.

FIGS. 12-14 illustrate an integrated circuit (IC) structure 270 having afin structure in accordance with some embodiments. FIG. 12 is a top viewof the IC structure 270 in accordance with some embodiments. FIG. 13 isa sectional view of the IC structure 270 along the dashed line AA′ inaccordance with some embodiments. FIG. 14 is a sectional view of the ICstructure 270 along the dashed line BB′ in accordance with someembodiments. The IC structure 270 includes a first fin active region 272and a second fin active region 274 formed on the semiconductor substrate210. The fin active regions 272 and 274 are extended vertically abovethe top surface of the STI features 212. The semiconductor material ofthe fin active regions may be same or alternatively different from thesemiconductor substrate 210. The fin active regions may be formed byetching to recess the STI features or by selective epitaxy growth. Inone embodiment, the first fin active region 272 is for a nFET and thesecond fin active region 274 is for a pFET. In furtherance of theembodiment, a p-type doped well 276 is formed in the first fin activeregion 272, and a n-type doped well 278 is formed in the second finactive region 274, such as by ion implantations. Accordingly, a firstchannel region 280 and a second channel region 282 are defined in thefirst and second fin active regions, respectively.

In some embodiments, the S/D features 230 are formed by epitaxy growthfor strain effect, such as those illustrated in FIG. 10. The gate stack220 is formed over the fin active regions. The gate stack 220 is similarto the gate stack 220 of FIG. 7, or one of FIGS. 8-11 in variousembodiments. In one embodiment when the active regions 272 and 274 aredifferent conductive types, the gate stack 220 includes two portions ofdifferent material stacks, such as a first portion over the first finactive region 272 and a second portion over the second fin active region274. Two portions are similar in composition except for the workfunction metal layer 244. In the first portion of the gate stack, thework function metal layer includes a nWF metal layer. In the secondportion of the gate stack, the work function metal layer includes a pWFmetal layer.

Although different embodiments are described. There are still otherembodiments of the integrated circuit device that combines two or moreabove embodiments. For example, one integrated circuit device includesboth epitaxy grown S/D features and a U-shaped high-k dielectric layer.In another example, one integrated circuit device includes both finactive region and with an additional capping layer 250.

A conventional gate stack includes a gate dielectric layer, a workfunction layer disposed over the gate dielectric layer; a blockinglayer, such as a tantalum nitride (TaN) blocking layer, disposed overthe work function layer; a wetting layer, such as a titanium (Ti)wetting layer, disposed over the blocking layer; and a conductive layer,such as an aluminum (Al) conductive layer, disposed over the wettinglayer. The TaN blocking layer provides less than desirable blockingcapability, and it has been observed that aluminum impurities from thealuminum conductive layer can penetrate the gate dielectric layer duringprocessing. Further, though the Ti wetting layer provides sufficientwettability to the Al conductive layer, it has been observed that phasetransformations occur between the Ti wetting layer and the Al conductivelayer during processing, leading to portions of the TaN blocking layerinteracting with Ti during processing, and eventually leading to missingportions of the TaN blocking layer (in other words, portions of the TaNblocking layer are consumed during processing). The missing portions ofthe TaN blocking layer further minimizes the TaN blocking layer'sability to prevent the aluminum impurities from penetrating the gatedielectric layer. Such phase transformations and missing portions of TaNblocking layer have also been observed when the gate stack includes atantalum aluminum (TaAl) wetting layer.

To address such issues, the present disclosure replaces the separate TaNblocking layer and Ti wetting layer of conventional gate stacks with theTaAlCN multi-function blocking/wetting layer 242. The blocking abilityof TaAlCN exceeds the blocking ability of TiN and TaN (specifically,blocking ability of TaAlCN>TaAlC>>TaN). Further, TaAlCN providessufficient wettability to an Al conductive layer. Accordingly, theTaAlCN multi-function blocking/wetting layer provide improved blockingability and wettability, leading to reduced leakage current and improveddevice performance, as compared to gate stacks including conventionalTaN blocking layer/Ti wetting layer. Particularly, TaAlCN is morechallenge than other materials, such as includes titanium aluminumcarbon nitride (TiAlCN), in terms of formation, particle/residualissues, which as addressed in the integrated circuit device 200 and themethod 100 making the same in accordance with various embodiments.Different embodiments may have different advantages, and that noparticular advantage is necessarily required of any embodiment.

The present disclosure provides for many different embodiments. In someembodiments, an integrated circuit device includes a semiconductorsubstrate; and a gate stack disposed over the semiconductor substrate.The gate stack further includes a gate dielectric layer disposed overthe semiconductor substrate; a multi-function blocking/wetting layerdisposed over the gate dielectric layer, wherein the multi-functionblocking/wetting layer comprises tantalum aluminum carbon nitride(TaAlCN); a work function layer disposed over the multi-functionblocking/wetting layer; and a conductive layer disposed over the workfunction layer.

In some other embodiments, an integrated circuit device includes asemiconductor substrate having a first region for a n-channel fieldeffect transistor and a second region for a p-channel channel fieldeffect transistor; a first gate stack disposed over the semiconductorsubstrate within the first region; and a second gate stack disposed overthe semiconductor substrate within the second region. The first gatestack includes a high-k dielectric layer disposed over the semiconductorsubstrate, a first tantalum aluminum carbon nitride (TaAlCN) layerdisposed over the high-k dielectric layer, and an n work function (nWF)metal layer with a first work function disposed directly on the firstTaAlCN layer. The second gate stack includes the high-k dielectric layerdisposed over the semiconductor substrate, the first TaAlCN layerdisposed over the high-k dielectric layer, and a p work function (pWF)metal layer with a second work function disposed directly on the firstTaAlCN layer, the second work function being greater than the first workfunction.

In yet some other embodiments, a method includes forming a gate stackover a semiconductor substrate; forming an interlayer dielectric (ILD)layer surrounding the gate stack; at least partially removing the gatestack, thereby forming an opening in the ILD layer; and forming amulti-function blocking/wetting layer, a work function layer over themulti-function blocking/wetting layer, and a conductive layer over thework function layer. The multi-function blocking/wetting layer, the workfunction layer, and the conductive layer fill the opening. Themulti-function blocking/wetting layer includes first tantalum aluminumcarbon nitride (TaAlCN) layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a gate stack over asubstrate by: depositing a gate dielectric layer over the substrate;depositing a multi-function layer over the gate dielectric layer,wherein the depositing the multi-function layer includes depositing afirst metal nitride material with a first nitrogen (N) concentration toform a first sub-layer of the multi-function layer over the gatedielectric layer and depositing a second metal nitride material with asecond N concentration to form a second sub-layer of the multi-functionlayer over the first sub-layer, wherein the first N concentration isgreater than the second N concentration; and depositing a work functionlayer over the multi-function layer.
 2. The method of claim 1, whereinthe depositing the multi-function layer over the gate dielectric layerincludes performing a physical vapor deposition process.
 3. The methodof claim 2, wherein the performing the physical vapor deposition processincludes tuning process parameters to set the first N concentration fromabout 5% to about 15% and the second N concentration from about 2% toabout 5%.
 4. The method of claim 3, further comprising depositing thefirst metal nitride material directly on the gate dielectric layer,wherein the second metal nitride material is deposited over the firstmetal nitride material.
 5. The method of claim 2, wherein the performingthe physical vapor deposition process includes using a precursor thatincludes tantalum, aluminum, carbon, and nitrogen.
 6. The method ofclaim 2, wherein the performing the physical vapor deposition processincludes using a precursor that includes titanium, aluminum, carbon, andnitrogen.
 7. The method of claim 1, wherein the depositing the gatedielectric layer includes depositing a high-k dielectric layer.
 8. Themethod of claim 1, wherein the depositing the multi-function layer andthe depositing the work function layer is performed after removing apolysilicon gate layer.
 9. A method comprising: forming a gate stackover a substrate; at least partially removing the gate stack, therebyforming an opening; depositing a multi-function layer in the opening,wherein the multi-function layer includes nitrogen and one of titaniumor tantalum; and depositing a work function layer over themulti-function layer, wherein the work function layer includes nitrogenand one of titanium or tantalum, and further wherein a concentration ofthe nitrogen of the work function layer is less than a concentration ofthe nitrogen of the multi-function layer.
 10. The method of claim 9,wherein the depositing the multi-function layer and the depositing thework function layer includes performing a physical vapor depositionprocess that implements a precursor that includes nitrogen and one oftitanium or tantalum, wherein the physical vapor deposition process istuned to set the concentration of the nitrogen of the work functionlayer from about 2% to about 5% and the concentration of the nitrogen ofthe multi-function layer from about 5% to about 15%.
 11. The method ofclaim 10, wherein the precursor further includes carbon when depositingthe multi-function layer, the method further comprising tuning thephysical vapor deposition process to set a concentration of carbon fromabout 5% to about 20%.
 12. The method of claim 10, wherein the precursorfurther includes aluminum when depositing the multi-function layer anddepositing the work function layer.
 13. The method of claim 9, furthercomprising depositing a high-k dielectric layer in the opening beforedepositing the multi-function layer.
 14. The method of claim 13, furthercomprising depositing a capping layer over the high-k dielectric layer,wherein the capping layer includes nitrogen and one of titanium ortantalum.
 15. The method of claim 9, wherein: the forming the gate stackover the substrate includes forming a high-k dielectric layer over thesubstrate, forming a capping layer over the high-k dielectric layer, andforming a polysilicon layer over the capping layer, wherein the cappinglayer includes nitrogen and one of titanium or tantalum; and the atleast partially removing the gate stack includes removing thepolysilicon layer, wherein the opening exposes the capping layer.
 16. Amethod comprising: forming a dummy gate stack over a substrate; andreplacing at least a portion of the dummy gate stack with a metal gatestack, wherein the replacing includes: depositing a multi-function layerthat includes nitrogen and one of titanium or tantalum, depositing awork function layer over the multi-function layer, wherein the workfunction layer includes nitrogen and one of titanium or tantalum, andfurther wherein a concentration of the nitrogen of the work functionlayer is less than a concentration of the nitrogen of the multi-functionlayer, depositing a conductive layer over the work function layer, andperforming a planarization process to remove any excess multi-functionlayer, work function layer, and conductive layer.
 17. The method ofclaim 16, further comprising tuning process parameters of the depositingof the multi-function layer and the depositing of the work functionlayer, such that the concentration of the nitrogen of the work functionlayer is lower than the concentration of the nitrogen of themulti-function layer.
 18. The method of claim 17, wherein theconcentration of the nitrogen of the work function layer is about 2% toabout 5% and the concentration of the nitrogen of the multi-functionlayer is about 5% to about 15%.
 19. The method of claim 16, wherein thedepositing the conductive layer includes depositing a conductivematerial that includes aluminum.
 20. The method of claim 16, wherein themulti-function layer and the work function layer further includealuminum.